Pressure adjustable electrophotographic printing machine transfer apparatus

ABSTRACT

An apparatus in which a developed image of electrostatically charged particles is transferred from an image bearing member to a sheet of support material. The sheet of support material is secured to a support arranged to be moved into contact with the image bearing member at a preselected force. A substantially constant potential difference is maintained between the image bearing member and sheet support. During contact, the potential difference between the image bearing member and the sheet support attract the electrostatically charged particles to the sheet of support material.

[4 1 Nov. 12, 1974 United States. Patent Draugelis et a1.

ass s R 96/12 Szostak et 355/3 R 3,706,489 12/1972 Moxness et a1. 3 729 311 4/1973 Langdon 3,751,156 8/1973 Primary Examiner-Robert P. Greiner Franklin Reese Victor; John Attorney, Agent, or FirmH. Fleischer; J. J. Ralabate; Wagner, Penfield, all of NY. Green [57] ABSTRACT An apparatus in which a developed image of electrostatically charged particles is transferred from an [73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Sept. 21, 1973 PP N05 399,578 image bearing member to a sheet of support material. The sheet of support material is secured to a support arranged to be moved into contact with the image bearing member at a preselected force. A substantially constant potential difference is maintained between the image bearing member and sheet support. During 464 L 1 m m 9 9 1 m a b 3 M 3 mm MS s m mh c Hr a e ms L l .M .w. U.mF HUN 555 [1:1

[56] References Cited contact, the potential difference between the image UNITED STATES PATENTS bearing member and the sheet support attract the electrostatically charged particles to the sheet of support material.

Ba1tazz1.. 96/1.4 Shelffo...l...............................96/14 6 Claims, 2 Drawing Figures 3,109,355 11/1963 Ritzerfeld et a1. 3,598,580 8/1971 3,627,523 12/1971 PATENTE HUN 2 I914 SHEET 2 OF 2 PRESSURE ADJUSTABLE ELECTROPHOTOGRAPHIC PRINTING MACHINE TRANSFER APPARATUS BACKGROUND OF THE INVENTION This invention relates generally to an electrophotographic printing machine and more particularly concerns an apparatus for transferring electrostatically charged particles from an image bearing member to a sheet of support material.

The process of electrophotographic printing involves the creation of an electrostatic latent image corresponding to an original document and the reproduction thereof in viewable form. In the process of electrophotographic printing, as disclosed in US. Pat. No. 2,297,691 issued to Carlson in 1942, a light image of an original document is projected onto the charged photoconductive surface. The light image selectively dissipates the charge on the photoconductive surface to create an electrostatic latent image of the original document thereon. A developer mix comprising electrostatically charged toner particles and coarser carrier granules is brought into contact with the electrostatic latent image. The toner particles are attracted electrostatically from the carrier granules to the latent image. Thereafter, the toner powder image developed on the photoconductive surface is transferred to a sheet of support material, such as plain paper, amongst others.

One method of transferring the toner powder image is disclosed in US. Pat. No. 2,807,233 issued to Fitch in 1957. As described therein, a sheet of support material is interposed between a conductive roller and a photoconductive surface having the toner powder image thereon. A charge of opposite polarity from the toner powder image is depositedon the back side of the sheet of support material. This charge attracts the toner powder image from the photoconductive surface to the support material.

In multi-color electrophotographic printing, it is necessary to convey a single sheet of support material repeatedly through a transfer station. This enables a plurality of toner powder images to be transferred, in su- V perimposed registration with one another, to the sheet of support material. Thus, a multi-color image may be created on the support material. In order to effect transfer, the sheet of support material on the transfer roll must be brought into contact with the toner powder image to electrostatically attract the toner powder image thereto. Both the potential applied to the transfer roll and the contact force between the photoconductive drum and transfer roll is critical to the efficient transfer of the developed toner powder image. Thus, various techniques are utilized for adjusting the pressure between the photoconductive drum and the transfer roll. By way of example, IBM Technical Disclosure Bulletin Volume 15, No. 12, page 3644, of May 1973, describes one such approach. As illustrated therein, a pressure roll is supported by a pair of movable yokes. The yokes move the pressure roll against an operating roll having a thin resilient layer. The yokes are supported by springs and a cam follower arrangement. Adjustment of the springs regulates the pressure applied between the operating roll and pressure roll. The foregoing technique is a trial and error approach requiring extensive mechanical adjustments until the requisite contact force between the photoconductive drum and transfer roll is obtained. Moreover, the cam assembly utilized to move the transfer roll from an operative position in contact with the photoconductive drum to an inoperative position spaced therefrom is periodic and is not sequenced to the machine timing.

Accordingly, it is the primary object of the present invention to improve the control mechanism utilized to regulate the pressure between the transfer roll and photoconductive drum employed in an electrophotographic printing machine.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there is provided an apparatus for transferring a developed image of electrostatically charged particles from an image bearing member to a sheet of support material.

Pursuant to the present invention, there is provided means for supporting the sheet of support material. Means are also provided for generating a substantially constant potential difference between the supporting means and the image bearing member. Solenoid means move the supporting means from an inoperative position spaced from the image bearing member to an operative position in contact therewith. At contact, the potential difference between the supporting means and the image bearing member attracts the developed image of charged particles from the image bearing member to the sheet of support material secured to the supporting means. Controlling means adjust the contact force between the supporting means and image bearing member to obtain efficient transfer of the developed image of electrostatically charged particles.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

FIG. 1 is a schematic perspective view of an electrophotographic printing machine incorporating the features of the present invention therein; and

FIG. 2 is a schematic perspective view of the transfer apparatus employed in the FIG. 1 printing machine.

While the present invention will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION For a general understanding of the disclosed multicolor electrophotographic printing machine in which the present invention may be incorporated, continued reference is had to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. FIG. 1 schematically illustrates the various components of the printing machine employed to produce multi-color copies from a colored original document. Although the transfer apparatus of the present invention is particularly well adapted for use in a multi-color electrophotographic printing machine, it should become evident from the following description that it is equally well suited for use in a wide 3 variety of printing machines and is not necessarily limited to the particular embodiment shown therein.

As depicted in FIG. 1, the electrophotographic print- .ing machine includes an image bearing. member comprising a drum having a photoconductive surface 12 entrained about and secured to the exterior circumferential surface thereof. Drum 10 is mounted rotatably on the machine frame and driven at a substantially constant angular velocity, in the direction of arrow 14, by a drive motor (not shown). As drum 10 rotates, photoconductive surface 12 passes sequentially through a series of processing stations. The drive motor rotates drum 10 at a predetermined speed relative to the other operating mechanisms of the printing machine. A timing disc (not shown) mounted in the region of one end of the shaft of drum 10 coordinates the timing of the various operations with the rotation of drum 10 to produce the proper sequence of events at the respective processing stations.

Initially, drum 10 rotates photoconductive surface 12 through charging station A. At charging station A, a corona generating device, indicated generally at 16, extends longitudinally in a transverse direction across photoconductive surface 12. This readily enables corona generating device 16 to spray ions onto photoconductive surface 12, thereby producing a relatively high, substantially uniform charge thereon. Preferably, corona generating device 16 is of the type described in U.S. Pat. No. 2,778,946 issued to Mayo in 1957.

After photoconductive surface 12 is charged to a substantially uniform potential, drum 10 rotates to exposure stationB. At exposure station B, a color filtered light image of original document 18 is projected onto charged photoconductive surface 12. Exposure station B includes a moving lens system, generally designated by the reference numeral 20, and a color filter mechanism shown generally at 22. A suitable moving lens system is disclosed in US. Pat. No. 3,062,108 issued to Mayo in 1962. Original document 18 such as a sheet of paper, book, or the like is placed face down upon transparent viewing platen 24. As depicted in FIG. 1, lamps 26- are adapted to move in a timed relationship with lens 20 and filter mechanism 22 to thereby scan successive incremental areas of original document 18 disposed upon platen 24. This produces a flowing light image of original document 18 which is projected onto charged photoconductive surface 12. During the exposure process, filter mechanism 22 interposes selected color filters into the optic light path of lens 20. The filter, interposed into the light path, operates on the light rays transmitted through lens 20 to record an electrostatic latent image on photoconductive surface 12 corresponding to a pre-selected spectral region of the electromagnetic wave spectrum, hereinafter referred to as a single color electrostatic latent image.

Thereafter, drum 10 rotates to development station C. At development station C, three individual developer units, generally indicated by the reference numerals 28, and 32, respectively, are arranged to render visible the electrostatic latent image recorded on photoconductive surface 12. Preferably, the developer units are all of a type generally referred to in the art as magnetic brush developer units. A typical magnetic brush developer unit employs a magnetizable developer mix having carrier granules and toner particles therein. In amagnetic brush developer unit, the magnetizable developer mix is continually brought through a directional flux field to form a brush of developer material. The developer mix is continually moving to provide fresh developer mix to the brush. The brush, in the magnetic brush developer unit, has a magnetic member with a mass of developer mix adhering thereto by magnetic attraction. The developer mix includes carrier granules having toner particles clinging thereto by triboelectric attraction. This chain-like arrangement of developer mix simulates the fibers of a brush. Development is achieved by bringing the brush of developer mix into contact with photoconductive surface 12. Each of the developer units 28, 30 and 32, respectively, apply toner particles to photoconductive surface 12. The toner particles are adapted to absorb light within a pre-selected spectral region of the electromagnetic wave spectrum corresponding to the wave length of light transmitted through filter 22. For example, a latent image formed by passing the light image through a green filter will record the red and blue portions of the spectrum as areas of relatively high charged density on photoconductive surface 12, while the green light rays will pass through the filter and cause the charge density on photoconductive surface 12 to be reduced to a voltage level ineffective for development. The charged areas are then made visible by applying green absorbing (magenta) toner particles to the latent image recorded on photoconductive surface 12. Similarly, a blue separation is developed with blue absorbing (yellow) toner particles, while a red separation is developed with red absorbing (cyan) toner particles. A typical development station employing a plurality of developer units, as illustrated in FIG. 1, is described in copending application Ser. No. 255,259, filed in 1972.

After development, the now visible toner powder image is advanced to transfer station D. The toner powder image adhering electrostatically to photoconductive station 12 is transferred to a sheet of support material 34. Support material 34 may be, amongst others, plain paper or a sheet of polysulfone thermoplastic material. Supporting means or a transfer drum, shown generally at 36, secures support material 34 releasably thereto for movement in a recirculating path therewith. Transfer drum 36 is adapted to rotate in the direction of arrow 38 in synchronism with drum 10 (in this case at substantially the same angular velocity therewith). Hence, a plurality of toner powder images may be transferred from photoconductive surface 12 to support material 34, each toner powder image being superimposed in registration with the prior one. Image transfer is achieved by electrically biasing transfer roll 36 to a potential having a sufficient magnitude and the proper polarity to attract electrostatically toner particles from the latent image recorded on photoconductive surface 12 to support material 34. Transfer drum 36 comprises an aluminum tube, preferably, having a layer of urethane cast thereabout. A polyurethane coating is sprayed over the layer of cast urethane. Voltage generating means or power supply 40 applies a direct current voltage to the aluminum tube via suitable means such as a carbon brush and brass ring assembly (not shown). The transfer voltage may range from about 1500 to about 4500 volts. Transfer drum 36 is substantially the same diameter as drum 1!) and is driven at substantially the same speed thereat. Contact between photoconductive surface 12 of drum l0 and transfer roll 36 with support material 34 interposed therebetween is regulated by the controlling means of the present invention. Preferably, the contact force ranges from about 0.5 pounds to about 1.0 pound linear force. The controlling means will be described hereinafter with reference to FIG. 2.

Referring now to the sheet feeding arrangement, a stack 42 of support material is disposed upon tray 44.

.A feed roll 46, in operative communication with retard roll 48 advances and separates the uppermost sheet from stack 42 disposed'on tray 44. The advancing sheet moves into chute 50 which directs it into the nip of register rolls 52. Thereafter, gripper mechanism 54 mounted on transfer drum 36 secures releasably support material 34 thereto. In this manner, support material 34 rotates in a recirculating path on transfer drum 36. After a plurality of toner powder images have been transferred to support material 34, in superimposed registration with one another, gripper 54 separates support material 34 from transfer drum 36. As transfer drum 36 rotates in the direction of arrow 38, a stripper bar 56 is interposed therebetween. This separates support material 34 from transfer drum 36. Thereafter, support material 34 advances on endless belt conveyor 58 to fixing station E.

At fixing station E, a fuser, indicated generally at 60, permanently affixes the toner powder image to support material 34. One type of suitable fuser is described in US. Pat. No. 3,498,592 issued to Moser in 1970. Support material 34 with the powder image affixed thereto, is, thereupon, advanced by conveyors62 and 64 to catch tray 66. Catch tray 66 is arranged to permit the machine operator to readily remove the completed multi-color copy from the printing machine.

The last processing station in the direction of rotation of drum 10, as indicated by arrow 14, is cleaning station F. As heretofore indicated, a preponderance of the toner particles are transferred to support material 34, however, some residual toner particles remain on photoconductive surface 12. Cleaning station F removes the residial toner particles from photoconductive surface 12. Initially, a cleaning corona generating device (not shown) neutralizes the remaining electrostatic charge on the residual toner particles and photoconductive surface 12. Thereafter, the residual toner particles are cleaned from photoconductive surface by rotating fibrous brush 66 in contact therewith. One type of suitablebrush cleaning device is described in US. Pat. No. 3,590,412 issued to Gerbasi in l97l.

Referring now to FIG. 2, the-transfer apparatus of the present invention is illustrated therein in greater detail. As shown in FIG. 2, transfer drum 36 is mounted rotatably in yoke 70. Yoke 70 is mounted preferably on the machine frame, depicted fragmentarily by rod 72. As shown in FIG. 2, transfer drum 36 is in the operative position contacting photoconductive surface 12 of drum 10. Transfer drum pivots from an inoperative position spaced from photoconductive surface 12 to the operative position in contact therewith. The foregoing movement of transfer drum 36 is achieved by solenoid 74. Solenoid 74 is mounted on the machine frame and has one end portion thereof connected to an elastic member or spring 76. The other end of spring 76 is connected to an elongated threaded member 78 which is secured to yoke 70 by nut 80. Resilient means or spring 82 is connected to yoke 70 and also to the machine frame. Spring 82 is extended to counterbalance the weight of transfer drum 36. Thus, transfer drum 36 is substantially free floating. The stroke of solenoid 74 will extend spring 76 and pivot transfer drum 36 about bar 72 into engagement with photoconductive surface 12. Solenoid 74 is adapted to have a stroke of about /2 inch. It should be noted that FIG. 2 depicts only one side of transfer roll 36 the other side being substantially identical thereto. A stop (not shown) locates transfer drum 36 in the inoperative position spaced from photoconductive surface 12 of drum 10. As shown in FIG. 2, spring 82 is secured to yoke by a threaded hook 84 secured to yoke 70 by nut 86. The extension of spring 82 is adjusted by rotating nut 86. In this manner, the moment applied by spring 82 about rod 72 is adjusted to substantially balance the moment applied thereabout by the weight of transfer drum 86. The contact force between photoconductive surface 12 and transfer drum 36 is adjusted by regulating the extension of spring 76. This is achieved by rotating nut so as to move threaded member 78 in or out as required. Thus, the extension of spring 76 is adjusted so that when solenoid 74 energizes, transfer drum 36 pivots about bar 72 into engagement with photoconductive surface 12 of drum 10 at the preselected force, i.e. a force preferably ranging from about 0.5 pounds to 1 pound. In this instance, the controlling means 88 for adjusting the contact force is achieved by spring 76, threaded member 78 and nut 80. As hereinbefore indicated, the extension of spring 76 is adjusted by movement of nut 80 which regulates the protrusion of threaded member 78 from yoke 70.

In recapitulation, it is apparent that the transfer apparatus of the present invention controls the force applied between the transfer drum and the photoconductive surface. In this manner, the potential applied to the transfer drum efficiently transfers the developed toner powder image from the photoconductive surface to the sheet of support material secured releasably therein.

It is, therefore evident that there has been provided in accordance with the present invention an apparatus for transferring a toner powder image developed on a photoconductive surface to a sheet of support material that fully satisfies the objects, aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

What is claimed is:

1. An apparatus for transferring a developed image of electrostatically charged particles from an image bearing member to a sheet of support material, including:

a frame;

a yoke mounted pivotably on said frame;

a transfer drum mounted rotatably in said yoke and arranged to have the sheet of support material secured releasably thereon for movement in a recirculating path therewith;

resilient means for applying a moment to said yoke arranged to balance the moment applied thereon by said transfer drum;

means for generating a substantially constant potential difference between said transfer drum and the image bearing member;

solenoid means operatively associated with said yoke and arranged to move said transfer drum from an inoperative position spaced from the image bearing member to an operative position in contact therewith, whereby the potential difference between said transfer drum and the image bearing member attracts the developed image of charged particles from the image bearing member to the sheet of support material secured to said transfer drum; and

means for controlling the force applied at contact between said transfer drum and the image bearing member to effect efficient transfer of the developed image of electrostatically charged particles. 2. An apparatus as recited in claim 1, wherein said controlling means includes:

an elongated threaded member having one end portion thereof secured movably to said frame; and

an elastic member interconnecting said solenoid means with the other end portion of said elongated member. 3. An'apparatus as recited in claim 2, wherein said controlling means further includes means threadly engaging one end portion of said elongated member and securing movably said elongated member to said frame, said securing means being arranged to adjust the length of said elongated member protruding from said frame, thereby regulating the extension of said elastic member so that the transfer drum contacts the image bearing member with the preselected force.

4. An electrophotographic printing machine, including:

a photoconductive member; means for charging said photoconductive member to a substantially uniform potential;

means for exposing said charged photoconductive member to a light image of an original document disposed in the printing machine, thereby recording an electrostatic latent image thereof on said photoconductive member;

means for developing the electrostatic latent image recorded on said photoconductive member with electrostatically charged particles;

a frame;

a yoke mounted pivotably on said frame;

a transfer drum mounted rotatably in said yoke and arranged to have a sheet of support material secured releasably thereon for movement in a recirculating path therewith;

resilient means for applying a moment to said yoke arranged to balance the moment applied thereon by said transfer drum;

' means for generating a substantially constant potential difference between said transfer drum and said photoconductive member;

solenoid means operatively associated with said yoke and arranged to move said transfer drum from an inoperative position spaced from said photoconductive member to an operative position in contact.

therewith, whereby the potential difference between said transfer drum and said photoconductive member attracts the developed image of charged particles from said photoconductive member to the sheet of support material secured to said transfer drum; and

means for controlling the force applied at contact between said transfer drum and said photoconductive member to effect efficient transfer of the developed image of electrostatically charged particles. 5. A printing machine as recited in claim 4, wherein said controlling means includes:

an elongated threaded member having one end portion thereof secured movably to said frame; and

an elastic member interconnecting said solenoid means with the other end portion of said elongated member.

6. A printing machine as recited in claim 5, wherein said controlling means further includes means threadably engaging one end portion of said elongated member and secure movably said elongated member to said frame, said securing means being arranged to adjust the length of said elongated member protruding from said frame, thereby regulating the extension of said elastic member so that said transfer drum contacts said photoconductive member with the preselected force. 

1. An apparatus for transferring a developed image of electrostatically charged particles from an image bearing member to a sheet of support material, including: a frame; a yoke mounted pivotably on said frame; a transfer drum mounted rotatably in said yoke and arranged to have the sheet of support material secured releasably thereon for movement in a recirculating path therewith; resilient means for applying a moment to said yoke arranged to balance the moment applied thereon by said transfer drum; means for generating a substantially constant potential difference between said transfer drum and the image bearing member; solenoid means operatively associated with said yoke and arranged to move said transfer drum from an inoperative position spaced from the image bearing member to an operative position in contact therewith, whereby the potential difference between said transfer drum and the image bearing member attracts the developed image of charged particles from the image bearing member to the sheet of support material secured to said transfer drum; and means for controlling the force applied at contact between said transfer drum and the image bearing member to effect efficient transfer of the developed image of electrostatically charged particles.
 2. An apparatus as recited in claim 1, wherein said controlling means includes: an elongated threaded member having one end portion thereof secured movably to said frame; and an elastic member interconnecting said solenoid means with the other end portion of said elongated member.
 3. An apparatus as recited in claim 2, wherein said controlling means further includes means threadly engaging one end portion of said elongated member and securing movably said elongated member to said frame, said securing means being arranged to adjust the length of said elongated member protruding from said frame, thereby regulating the extension of said elastic member so that the transfer drum contacts the image bearing member with the preselected force.
 4. An electrophotographic printing machine, including: a photoconductive member; means for charging said photoconductive member to a substantially uniform potential; means for exposing said charged photoconductive member to a light image of an original document disposed in the printing machine, thereby recording an electrostatic latent image thereof on said photoconductive member; means for developing the electrostatic latent image recorded on said photoconductive member with electrostatically charged particles; a frame; a yoke mounted pivotably on said frame; a transfer drum mounted rotatably in said yoke and arranged to have a sheet of support material secured releasably thereon for movement in a recirculating path therewith; resilient means for applying a moment to said yoke arranged to balance the moment applied thereon by said transfer drum; means for generating a substantially constant potential difference between said transfer drum and said photoconductive member; solenoid means operatively associated with said yoke and arranged to move said transfer drum from an inoperative position spaced from said photoconductive member to an operative position in contact therewith, whereby the potential difference between said transfer drum and said photoconductive member attracts the developed image of charged particles from said photoconductive member to the sheet of support material secured to said transfer drum; and means for controlling the force applied at contact between said transfer drum and said photoconductive member to effect efficient transfer of the developed image of electrostatically charged particles.
 5. A printing machine as recited in claim 4, wherein said controlling means includes: an elongated threaded member having one end portion thereof secured movably to said frame; and an elastic member interconnecting said solenoid means with the other end portion of said elongated member.
 6. A printing machine as recited in claim 5, wherein said controlling means further includes means threadably engaging one end portion of said elongated member and secure movably said elongated member to said frame, said securing means being arranged to adjust the length of said elongated member protruding from said frame, thereby regulating the extension of said elastic member so that said transfer drum contacts said photoconductive member with the preselected force. 